class_docstr: Tests MergeLayer.
      
docstr: Tests MergeLayer.compute_output_shape function.
          
docstr_tok: ["Tests","MergeLayer.compute_output_shape","function","."]
code: def test_output_shape(self):
      """Tests MergeLayer.compute_output_shape function."""
      input_shapes = [[None, 1, 2], [64, 2, 2], [None, 3, 2]]
  
      concat_layer = layers.MergeLayer(mode="concat", axis=1)
      concat_output_shape = concat_layer.compute_output_shape(
          input_shapes
      )
      self.assertEqual(concat_output_shape, [64, 6, 2])
  
      sum_layer = layers.MergeLayer(mode="sum", axis=1)
      sum_output_shape = sum_layer.compute_output_shape(input_shapes)
      self.assertEqual(sum_output_shape, [64, 2])
  
      input_shapes = [[None, 5, 2], [64, None, 2], [2]]
      esum_layer = layers.MergeLayer(mode="elemwise_sum")
      esum_output_shape = esum_layer.compute_output_shape(input_shapes)
      self.assertEqual(esum_output_shape, [64, 5, 2])
  
imports: import numpy
  import tensorflow
  import tensorflow.contrib.rnn
  import texar.tf
  from texar.tf import context
  from texar.tf.hyperparams import HParams
  from texar.tf.core import layers
label_desc: Use image node_id 1 for calling the MergeLayerTest obj's underlying member method code with example usage: obj.test_output_shape() without return types